This invention relates to a lift truck control system and, more particularly, to improvements in a lift truck control system for causing a lift operation of clamping a cylindrical heavy object, e.g., a paper roll in a warehouse, for instance, rotating in this state, transporting the object in either longitudinal or transversal direction and unloading the object.
The lift truck of the type noted uses various attachments. Basically, attachments comprise a clamp and a rotator for rotating the clamp. Where a cylindrical heavy object such as a paper roll is handled for transport, a roll clamp is used. The clamp clamps the cylindrical object and, in this state, is set by the rotator to an angle position suited for the transport of the clamped object. In this way, loading and unloading operations are performed. Where such operation is performed with a fork lift, the clamp angle is controlled to permit clamping of the object, and also the angular position of the clamp is set such that the object can be readily clamped. A clamp operation is executed by bringing the clamp to a position to clamp the object. In this case, the clamp pressure is controlled such that the object is reliably clamped and raised. If the clamp pressure is too low, the object can not be stably supported. If the pressure is excessive, on the other hand, the object is liable to be damaged. Therefore, it is necessary to set an optimum clamp pressure depending on the weight and mechanical strength of the object.
In other words, to perform an operation of moving large, heavy and cylindrical objects to stack them in a warehouse using a fork lift, very high degrees of skill and decision are required. In addition, even if the operation is performed very carefully, the operation is greatly dangerous, and there are problems in connection with the improvement of the operation efficiency.